You can't.
I have done the same recently. I realized I wouldn't have enough money in my account to cover the transaction.
So I had to cancel the purchase.
Well you can't because it is not an option if it has been sent.
(mine was already gone, and showed pending status)
I even contacted the SELLER and THEY were nice enough to have cancelled the purchase.
So I thought the issue was closed.
NOPE!!
Paypal went ahead and continued to take money out of my account.
This cost me a NSF charge for a purchase that was cancelled.
I'm actually ON the phone right now trying to resolve the issue.
But so far, they don't seem to even get that it was a PAYPAL internet purchase, not my PAYPAL credit card, or PAYPAL debit card..
Cancelling something here doens't actually cancel it aparently.
So good luck.
You will be billed by your bank, and paypal will do nothing to help.
Make sure you have money in the account to cover it, that's all you can do.
